1. Field of the Invention
The present invention relates to a control system and, more particularly, to a control system suitable for application to control using a fuzzy inference.
2. Related Background Art
In the field of various control, recently, a so-called fuzzy inference is used which enables control in a natural manner and is flexibly adaptable to different situations by taking into account ambiguity, thereby achieving better control. For example, U.S. patent application Ser. No. 578,024 and U.S. patent application Ser. No. 580,195 filed by the present applicant on Sep. 5, 1990 and Sep. 10, 1990, respectively, employ the fuzzy inference.
In a control system of this type, a degree to which a plurality of data associated with control conform with preset conditions is determined using a predefined membership function. The control amount is computed from the determination result and a predefined output function.
Namely, a plurality of control data are detected, substituted in a membership function which is prepared in advance, and collated with preset rules. A degree to which the detection data conforms with the rules is calculated in a quantitative manner. The calculation result is substituted in the membership function to produce an output membership function suitable for various situations, thus computing the control amount. More particularly, a computation is finally performed to obtain the centroid of the external figure of the output membership function, thus obtaining a control output that reflects various ambiguities.
In this manner, the control utilizing the fuzzy inference is composed of steps of membership function development, rule (conditions) determination, non-fuzzy processing for computing the control amount, and the like.
Other various types of apparatuses can be control targets having ambiguities. In the field of, e.g., the imaging apparatus such as a video camera, if a system is used in considerably various situations and the user needs to make decisions depending on his sense, as in a focusing system, it is highly effective to perform control with human factors that utilize the ambiguities described above.
Control of this type is effective not only in the imaging apparatus but can be applied to any apparatus in any field regardless of the types of control targets. Reduction in size and cost of the control system is necessary in any field, especially in the field of small commercial electronic appliances such as home electronics.
However, according to the control system described above, if the fuzzy inference is used in control, a comparatively large-scale system is required for development of the membership function, rule (conditions) determination, a non-fuzzy process for computing the control amount, and so on. This is because development of the membership function and the non-fuzzy process for computing the control amount require most advanced, complicated computation.
More particularly, the centroid of the external figure of the output membership function is calculated in the non-fuzzy process, thereby obtaining the final result. The external figure of the output membership function changes according to the rule conforming conditions and is usually very complicated. Accordingly, computation for obtaining the centroid of the external figure is very complicated and cannot be performed with ease.
Along with recent size reduction of various apparatuses, it has become more and more necessary to perform the fuzzy inference in a software manner by utilizing a one-chip microcomputer. When a one-chip microcomputer is used to accurately perform the above-described centroid computation, however, a serious problem arises as the program capacity and the processing speed are limited.